Generally, in manufacturing a semiconductor device, a liquid crystal display device, and the like, ultrapure water (UPW) (including ultrapure water containing hydrogen or ozone, i.e., so-called hydrogen water or ozone water) is often transported and supplied through a resin tube (resin pipe), as well as various chemical solutions. As mentioned above, ultrapure water is used in manufacturing the semiconductor device or the like. This is because, if water used in a cleaning process and the like contains a large amount of oxygen in the form of dissolved oxygen, a natural oxide film is formed by the dissolved oxygen. In recent years, it is pointed out that, even when ultrapure water is used, the natural oxide film is similarly formed. Therefore, it is practiced to completely remove oxygen, particles, and metal components in ultrapure water.
For example, when the semiconductor device is manufactured using a silicon crystal, coexistence of oxygen and water causes the natural oxide film (SiOx) to be formed on a silicon surface. Especially, it is also pointed out that, if oxygen is contained in an aqueous solution, the silicon surface is oxidized and etched to increase surface microroughness.
In recent years, attention is drawn to a Si (110) crystal surface which has a higher current drive capability of a PMOSFET than that of a Si (100) crystal surface. However, such surface is severely etched in an aqueous solution as compared to the Si (100) surface. In general, the silicon surface is cleaned by wet cleaning using the aqueous solution. In that case, for the above-mentioned reason, it is required to prevent oxygen from being mixed into the aqueous solution.
Herein, it is pointed out that mixture of oxygen into the aqueous solution occurs not only during processing, such as in a cleaning process, but also in the resin tube forming a transport line for ultrapure water, a chemical solution, and the like.
In order to reduce mixture of oxygen in the transport line, Patent Document 1 discloses a resin tube comprising a resin tube body and a heat-shrinkable strip-like film which is formed of a resin capable of suppressing gas permeation and spirally wound around the resin tube body so that parts of the film overlap with each other. In Patent Document 1, the wound-around strip-like film is heated in a vacuum atmosphere at a temperature lower than a melting point of the strip-like film to cause heat shrinkage and fusion-bonding of the wound-around strip-like film, thereby excluding air between the parts of the wound-around film. Further, Patent Document 1 discloses that, as the tube body, a fluororesin, such as a tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), a polytetrafluoroethylene resin (PTFE), and a tetrafluoroethylene-hexafluoropropylene copolymer (FEP), is used. Furthermore, it is also disclosed that, as the strip-like film, polyvinylidene chloride which has a low gas permeation rate and a heat-shrinkable characteristic is used. Thus, the strip-like film forms a gas permeation suppressing outer coating layer to thereby prevent a gas from permeating the outer coating layer and being dissolved into ultrapure water or a chemical solution flowing through the tube.
On the other hand, Patent Document 2 discloses, as a resin tube for use in a semiconductor manufacturing device, a liquid crystal manufacturing device, and the like, a fluororesin double tube comprising two laminated layers of fluororesin. The fluororesin double tube disclosed in Patent Document 2 comprises an inner layer tube and an outer layer tube. The inner layer tube is formed of a fluororesin excellent in corrosion resistance and in chemical resistance (for example, a tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), a tetrafluoroethylene-hexafluoropropylene copolymer (FEP), or a tetrafluoroethylene-ethylene copolymer (ETFE)). The outer layer tube is formed of a fluororesin capable of suppressing gas permeation (for example, polyvinylidene-fluoride (PVDF)). The fluororesin double tube has a structure in which the inner layer tube and the outer layer tube are welded to each other.
The fluororesin double layer tube disclosed in Patent Document 2 is excellent in corrosion resistance, in chemical resistance, and in gas impermeability and is advantageous in that the inner layer tube and the outer layer tube can firmly be joined to each other.
Patent Document 1: JP-A-2004-322387
Patent Document 2: JP-A-2006-112507